The goal of this research proposal is to determine the role gammadelta T cells play in microbial immunity. Although their biological function remains unclear, the chronic inflammation and tissue necrosis that occurs in virus- bacteria- and parasite- infected gammadelta T cell deficient mice suggest that gammadelta T cells are important in resolving inflammation and preventing the development of chronic disease. However, little is known about how gammadelta T cell responses are regulated, or the nature of the cells and antigens they react with in vivo. Using established mouse models of infectious disease we have shown that gammadelta T cells are involved late in the immune response to viruses and bacteria, coincident with pathogen clearance. Their involvement is dependent upon the elicitation of macrophages (Mphi) expressing high levels of mRNA encoding the 60kDa heat shock protein (HSP60). The gammadelta "response" is also characterized by the predominance of cells expressing a TCR encoded by a single Vgamma (Vgamma1) and Vdelta (Vdelta6.3) chain, concordant with the TCR phenotype of HSP60- reactive hybridomas described by others. Based upon these studies we propose that Vgamma1/Vdelta6.3 T cells are reactive with pathogen-elicited (HSP60 plus) Mphi and as a result of this interaction activated Vgamma1/Vdelta6.3 T cells promote the generation and maintenance of Mphi with antiinflammatory properties that are essential for resolving inflammation and preventing chronic disease. An experimental mouse model of Listeriosis will be used to test this hypothesis. The first specific aim is to identify Listeria-elicited Mphi that can stimulate Vgamma1/Vdelta6.3 T cells and to determine if HSP60 mediates this cell-cell interaction. Peritoneal exudate cells (PEC) elicited in response to Listeria-infection will be screened for their ability to activate and induce cytokine production by bulk and clonal populations of Vgamma1/Vdelta6.3 T cells. The functional properties of stimulatory PEC will be established and these cells used to isolate HSP60. The second specific aim is to determine if Vgamma1/Vdelta6.3 can influence the functional properties of Listeria-elicited (HSP60 plus) Mphi. The requirement for gammadelta and Vgamma1/Vdelta6.3 T cells for the generation of antiinflammatory Mphi will be investigated by determining what the outcome of infecting gammadelta-deficient and scid mice with Listeria, or scid mice transduced with Vgamma1/Vdelta6.3 T cells is for Mphi activity. Co-culture assays will also be used to determine if, and by what mechanism, Vgamma1/Vdelta6.3 T cells can modulate the development and functional phenotype of in vitro-generated and in vivo pathogen- elicited Mphi. The possibility that the survival, growth and functional properties of Vgamma1/Vdelta6.3 T cells are changed as a consequence of their interaction with HSP60-expressing macrophages will also be investigated. These studies should provide new and important insights into the biological function of gammadelta T cells, and increase our understanding of the pathogenesis of severe and persistent inflammation that is a hallmark feature of chronic infection and autoimmune disease.